Hitting the g-spot

I want to try fingering my girl friend some time soon and I want to make it as pleasurable as possible for her. I've heard that I can massage her G-spot while licking her clit and that will drive her absolutely nuts with pleasure.

How do I find the g spot, apparently it's about 2 inches into the vagina and on the upper wall. Will it be obvious when I hit it, like does it feel different or will she immediately react?

Also about how long will it take for her to have an explosive orgasm after I start? 5 minutes, 10 minutes? longer?

Thanks

as a holder of a vagina i can vouch geeks know what they are talking about! geeks are the best fuckers ever! the lack of women makes them last longer and be more powerful in the bedroom. the excessive porn was a learning tool thus they know all the moves and a lot of geek have nice bodies and are really hot under those glasses.

that and many other reasons make me only date geeks or otaku.